LeetCode OJ：Majority Element II（主元素II）

Given an integer array of size n, find all elements that appear more than ⌊ n/3 ⌋ times. The algorithm should run in linear time and in O(1) space.

求主元素，这次的是大于sz/3就算是主元素，可以分为两轮查找，第一轮先查找元素数目较多的两个元素（可能不属于主元素），第二次再遍历来查找上面两个元素是否符合条件，代码如下：

class Solution {
public:
    vector<int> majorityElement(vector<int>& nums) {
        int m1, m2;
        int count1, count2;
        vector<int> ret;
        int sz = nums.size();
        if(!sz) return ret;
        m1 = nums[0];
        m2 = 0;
        count1 = 1;
        count2 = 0;
        for(int i = 1; i < sz; ++i){
            if(m1 == nums[i])
                count1++;
            else if(m2 == nums[i])
                count2++;
            else if(count1 == 0){
                count1++;
                m1 = nums[i];
            }else if(count2 == 0){
                count2++;
                m2 = nums[i];
            }else{
                count1--;
                count2--;
            }
        }
        count1 = count2 = 0;
        for(int i = 0; i < sz; ++i){
            if(nums[i] == m1) ++count1;
            if(nums[i] == m2) ++count2;
        }
        if(count1 > sz/3) ret.push_back(m1);
        if(m1 != m2)
            if(count2 > sz/3) ret.push_back(m2);
        return ret;
    }
};